Abstract
Abstract. The Lake Urmiah has undergone a drastic shrinkage in size over the past few decades. The initial intention of this paper is to present an approach for determining the so called “salient times” during which the trend of the shrinkage process is accelerated or decelerated. To find these salient times, a quasi_continuous curve was optimally fitted to the Topex altimetry data within the period 1998 to 2006. To find the salient points within this period of time, the points of inflections of the fitted curve is computed using a second derivative approach. The water volume was also computed using 16 cloud free Landsat images of the Lake within the periods of 1998 to 2006. In the first stage of the water volume calculation, the pixels of the Lake were segmented using the Automated Water Extraction Index (AWEI) and the shorelines of the Lake were extracted by a boundary detecting operator using the generated binary image of the Lake surface. The water volume fluctuation rate was then computed under the assumption that the two successive Lake surfaces and their corresponding water level differences demonstrate approximately a truncated pyramid. The analysis of the water level fluctuation rates were further extended by a sinusoidal curve fitted to the Topex altimetry data. This curve was intended to model the seasonal fluctuations of the water level. In the final stage of this article, the correlation between the fluctuation rates and the precipitation and temperature variations were also numerically determined. This paper reports in some details the stages mentioned above.
Highlights
The factors that have contributed to the shrinkage of the Lake Urmiah have been well investigated in recent years (Hassanzadeh et al, 2012; Karimi and Mobasheri, 2011; Khatami Mashhadi, 2013; Wurtsbaugh et al, 2014)
These points are regarded as the indicators of the beginning or the terminating phases of an anomaly. These salient points can be employed to find out the statistical correlation and the contributing rate of the factors that are responsible for the shrinkage of the Lake
The initial intention of this paper is to present an approach for the determination of these salient points
Summary
The factors that have contributed to the shrinkage of the Lake Urmiah have been well investigated in recent years (Hassanzadeh et al, 2012; Karimi and Mobasheri, 2011; Khatami Mashhadi, 2013; Wurtsbaugh et al, 2014) These influential factors are mainly related to the following causal elements: the drought; the decreased flow of the main rivers of the Lake’s drainage basin due to the civil engineering projects such as dam constructions; the change of agricultural crops into those with higher water consumption requirements; bridge construction over the Lake; and increased rate of the drilled water wells. The first stage to achieve this goal is to find out the exact time of the occurrences of the so called ‘salient times’ within the water level fluctuation time series These points are regarded as the indicators of the beginning or the terminating phases of an anomaly. The values 0 and 1 denote the lake and the land surfaces respectively
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